When I arrived at work I went upstairs doing single leg step-ups thus completing my basic strength routine from yesterday. I left work a little early and went for a swim. The pool was very quiet and so there was no excuse for my slow progress. I do believe that I kept my form reasonably tidy throughout the 1.2km and was aware of time when quality slipped.
Until leaving for home I'd had little awareness of knee pain but during the walk home the left knee especially felt tired and with a little soreness. This can't have been anything severe as it wasn't obvious during a short walk in the evening.